The long-term goal of this proposal is to understand the mechanism of. Our present understanding of the pathogenesis of cholestasis is based on studies to define the physiological regulation of transporters involved in bile formation and their deregulation in cholestasis. During the last granting period we have defined the role of aPKC , Rab4 and phosphorylation in Ntcp translocation and started defining the role of nPKC , nPKC and p38 MAPK in Mrp2 translocation. The present proposal extends these studies to further define the role of nPKC and nPKC in Ntcp/NTCP and Mrp2/MRP2 translocation/retrieval. One of the key goals is to define the mechanism involved in opposing effects of these kinases in hepatocytes. The following hypotheses are proposed: 1) nPKC -pThr505 mediates translocation of Ntcp/NTCP by cAMP and translocation of Mrp2/MRP2 by cAMP and TUDC to the plasma membrane, 2) nPKC mediates TLC-induced retrieval of Mrp2/MRP2 from the plasma membrane by phosphorylating MARCKS and/or Mrp2/MRP2, and cAMP and TUDC reverse this effect by inhibiting TLC-induced nPKC activation. Proposed studies will be conducted in perfused livers and hepatocytes from rat livers, primary human hepatocytes and hepatic cell lines. In addition, studies will be conducted in perfused livers and hepatocytes isolated from nPKC -/- and nPKC -/- mice to further confirm the role of these kinases. Role of these kinases will be evaluated by manipulating their activity and expression using chemical inhibitors, wild type-, constitutively active- and dominant negative-plasmids and Si- and/or ShRNA. Immunofluorescence and co-immunoprecipitation studies will be used to determine colocalization of desired proteins in subcellular organelles and with other proteins. Collectively, proposed studies should further define the role of nPKC in Ntcp/NTCP and Mrp2/MRP2 translocation, the role of nPKC in Mrp2/MRP2 retrieval, and mechanism of reversal of TLC-induced cholestasis by cAMP and TUDC. Since a kinase may produce beneficial or toxic effect in an isoform specific manner, a better understanding of isoform specific effects should allow for better therapeutic agents that could avoid potential liver toxicity.